Image intensifier devices multiply the amount of incident light they receive and provide an increase in light output, which can be supplied either to a camera or directly to the eyes of a viewer. These devices are particularly useful for providing images from dark regions and have both industrial and military applications. For example, image intensifier tubes are used for enhancing the night vision of aviators, for photographing astronomical bodies and for providing night vision to sufferers of retinitis pigmentosa (night blindness). Such an image intensifier device is exemplified by U.S. Pat. No. 5,084,780, entitled TELESCOPIC SIGHT FOR DAY/NIGHT VIEWING by Earle N. Phillips issued on Jan. 28, 1992 and assigned to ITT Corporation the assignee herein.
Modern image intensifier tubes include three main components, namely a photocathode, a phosphor screen (anode) and a microchannel plate (MCP), disposed between the photocathode and anode. All three components are formed within an evacuated housing thereby permitting electrons to flow from the photocathode, through the MCP and to the anode. In order for the image intensifier tube to operate, the photocathode and anode must be coupled to an electric source whereby the anode is maintained at a higher positive potential than is the photocathode. Similarly, the microchannel plate must be empowered to increase the density of the electron emission set forth by the photocathode. Furthermore, since the photocathode, MCP and anode are all held at different electrical potentials, all three components must be electrically isolated from one another when retained within the vacuum housing.
In some prior art image intensifier tubes, the vacuum housing of the tube is constructed by the juxtaposition of conductive elements and dielectric elements. When assembled, the photocathode, MCP and anode engage the conductive elements within the vacuum housing. As such, an electric potential can be supplied to the photocathode, MCP and anode within the vacuum housing through the material of the vacuum housing itself. The dielectric elements juxtaposed between the conductive elements, isolates the photocathode, MCP and anode from one another, while the assemblage of the conductive and dielectric elements create the overall evacuated chamber of the image intensifier tube. Since the vacuum housings of such prior art image intensifier tubes are formed of both conductive and dielectric elements, the prior art housings can not be manufactured from a single material. Rather, the conductive elements and dielectric elements of such prior art vacuum housings must be formed separately and later joined to form the needed structure. Such prior art image intensifier tube housings therefore require multiple manufacturing tools and procedures to form and assemble the various conductive and dielectric elements. Furthermore, the various conductive and dielectric elements must be joined in an air tight manner so as to form the needed vacuum integrity. The complex manufacturing process and assembly procedure needed to produce such prior art vacuum housings add significantly to the cost at which such prior art image intensifier tubes can be manufactured. Additionally, since multiple joints exist between the various conductive and dielectric housing elements, there exist many points at which a vacuum leak may occur. Consequently, forming image intensifier tube housings from several juxtaposed components reduces the overall reliability of the image intensifier tube.
In view of the prior art, there exists a need for an image intensifier tube that has a housing that is simple to manufacture, has a reliable vacuum integrity and electrically isolates the photocathode, MCP and anode from each other while allowing each to be coupled to a source of electrical potential outside of the assembled image intensifier tube.